Ultimately from Proto-Yoruba *è-dè. While the semantic meaning of language and this specific form is restricted to Proto-Yoruba, the root is widespread across Niger-Congo as roots for "tongue," and thus derives from an older stem. That older stem may be Proto-Yoruboid *-dè. The stem likely originally meant tongue, language, and the general mouth area, but became restricted for language (and also became the term for lip), and replaced ohùn. This is almost certainly a Doublet of ètè. This also explains why the Proto-Yoruboid word for tongue is likely an innovation, see *ʊ́-ɓã́ (“tongue”), see ahọ́n (“tongue”). Compare with Proto-Edoid *U-dhamhɪ, Ibibio edeme, Proto-Bantu *dʊ̀dɪ́mì, Proto-Jukunoid *dema. Many other Yoruba-dialects also have different terms for the language, see eréùn in Ijebu.